Control system for hybrid vehicle

Abstract

A control system for hybrid vehicles configured to improve an acceleration feeling or enhance acceleration. In the hybrid vehicle, an engine and a first motor are connected to an input side of a transmission, and a second motor is connected to drive wheels. A controller is configured to selectively execute a first assist control to raise an input speed to the transmission by the first motor, and a second assist control to increase an output torque of the second motor, depending on a required drive force.

What is claimed is: 
     
       1. A control system for a hybrid vehicle in which an engine and a first motor are connected to an input side of an automatic transmission, and a second motor is connected to drive wheels, comprising:
 a controller that controls the first motor and the second motor, 
 wherein the controller is configured to
 calculate a required drive force, 
 execute a selective control to selectively execute a first assist control to raise an input speed to the automatic transmission by the first motor, and a second assist control to increase an output torque of the second motor thereby increasing the drive force to propel the hybrid vehicle, based on the required drive force, 
 execute an acceleration demand determination to determine whether a driver intends to accelerate the hybrid vehicle, 
 execute a drive force determination Whether the output torque possible to b generated by the second motor is insufficient to achieve the required drive force to accelerate the hybrid vehicle, after executing the acceleration demand determination, 
 select the first assist control when the output torque possible to be generated by the second motor is insufficient to achieve the required drive force, and 
 select the second assist control when the second motor is allowed to generate the output torque to achieve the required drive, 
 
 wherein the acceleration demand determination is made based on an increase in the required drive force and a condition to execute a downshift is satisfied, and 
 wherein the first assist control is executed to expedite execution of a downshifting by raising the input speed by the first motor. 
 
     
     
       2. The control system for the hybrid vehicle as claimed in  claim 1 , wherein the drive force determination is made based on a fact that a speed of the hybrid vehicle is higher than a reference speed. 
     
     
       3. The control system for the hybrid vehicle as claimed in  claim 1 , wherein the drive force determination includes a determination whether a speed of the hybrid vehicle is higher than a reference speed, and the required drive force was constant to cruise the hybrid vehicle immediately before the acceleration is demanded. 
     
     
       4. The control system for the hybrid vehicle as claimed in  claim 1 , further comprising:
 an electric storage device that supplies electricity to the first motor and the second motor, 
 wherein the drive force determination includes a determination whether a state of charge level of the electric storage device is lower than a level at which the second motor is allowed to generate a required power to execute the second assist control. 
 
     
     
       5. The control system for the hybrid vehicle as claimed in  claim 1 , wherein the controller is further configured to inhibit execution of the second assist control by the second motor during execution of the first assist control by the first motor. 
     
     
       6. The control system for the hybrid vehicle as claimed in  claim 1 , wherein the controller is further configured to stop electric power supply to the second motor when raising the input speed by the first motor. 
     
     
       7. The control system for the hybrid vehicle as claimed in  claim 1 , wherein the controller is further configured to
 determine whether the downshifting to be executed in response to an increase in the acceleration demand is a step shifting to shift a gear stage of the automatic transmission to a target stage that is two or more stages lower than the current stage via an interim stage, 
 execute the first assist control to expedite execution of the downshifting by raising the input speed to the automatic transmission by the first motor until the completion of the downshifting, if execution of the step shifting is determined, and 
 execute the second assist control to drive the second motor when shifting the gear stage from the interim stage to the target stage. 
 
     
     
       8. The control system for the hybrid vehicle as claimed in  claim 1 ,
 wherein the hybrid vehicle comprises front wheels to which the second motor is connected, rear wheels to which the torque is delivered from the automatic transmission, and a transfer that delivers the torque delivered from the automatic transmission to the front wheels, and 
 the second motor is connected to the transfer.